September 16 is actually Mexico’s Independence Day from Spain back in 1810. There are many resources which explain what Cinco de Mayo actually is, it’s History and how it has become a reason to Party. Mexico has a Long, Beautiful, Vibrant History and Culture and May 5th is hardly representative of it.
Today is also reason for mostly Non-Mexicans as pictured above to Drink, Party and dress up as “Mexicans”. Call it cultural appropriation, just having Fun or any other reason, whatever you want to view it as, this is unfortunately just another example of how ignorant Human beings can be.